The long-term goal of this project is to provide new information regarding the development, function, and plasticity of hypothalamic magnocellular neurosecretory cells. The specific aims of the proposed research build upon recent accomplishments in our laboratory. A library of monoclonal antibodies (MAbs) which bind to cell bodies and/or terminals of neurosecretory neurons has been produced. The primary aim is to characterize the cellular, ultrastructural, and biochemical specificity of these MAbs using light microscopic and EM immunocytochemistry and gel- electrophoresis - immunoblotting. Successful isolation of MAbs specific for cell surface molecules of neurosecretory cells may make it possible to test several specific hypothesis. Among these are: (1) that specific cell surface molecules mediating strict chemoaffinity mechanisms play a more important role that competitive rearrangement of circuitry during hypothalamic-neurohypophysial developments; (2) that glucocorticoids and other hormonal or trophic factors influence cell survival and/or peptide gene expression during neurosecretory differentiation; and, (3) that alterations in the expression of plasmalemmal molecules mediate the marked plastic changes which occur in the mature magnocellular system as a result of injury or intense activation. This project represents an excellent opportunity for MBRS student participation because of the diversity of biochemical and immunocytochemical techniques involved, and because the large number of MAbs which have been generated make it possible for the student to define his or her own unique experiments.